Why is friction essential ?

Why is thyroxin essential in humans ?

Why is it essential to wash the precipitate with water before estimating it quantitatively?

Why does friction increase if the two surfaces are pressed ?

Why are vitamin A and vitamin C essential to us? Give their important sources.

Explain why friction is necessary to make the disc in Fig. 7.41 roll in the direction indicated. (a) Give the direction of frictional force at B, and the sense of frictional torque, before perfect rolling begins. (b) What is the force of friction after perfect rolling begins?

Name one lectin and one essential oil in plants.

Define friction.